1. Field of the Invention
The present invention relates to electric sockets and more particularly, to an electric socket having means to lock the blades of inserted electric plug.
2. Description of the Related Art
An electric socket is an important electric connector for the insertion of an electric plug to obtain power supply. Many electric socket patents have been issued. Taiwan Utility Patent No. M261875, issued on Apr. 11, 2005, discloses an electric socket, entitled “Electric Socket Locking Structure”, which comprises a housing 1, a socket body 2 and a locking device 3. By means of rotating the knob 31 of the locking device 3 to press the protruding portions 314 of the knob 31 on top blocks 323 of a holding down member 32, protruding blocks 332 of a retaining member 33 that is rotated by the knob 31 are respectively moved over the protruding blocks 324 of the holding down member 32 into a respective groove 322 on the bottom wall of the holding down member 32, allowing an arched face 311 of the knob 31 to force the holding down member 32 downwards. At this time, pressure feet 325 of the holding down member 32 are lowered to force respective bottom grooves 326 thereof into engagement with the metal conducting blades 61 of the inserted electric plug 6. When reversing the knob 31 of the locking device 3, the protruding blocks 332 of the retaining member 33 are moved out of the grooves 322 over the protruding blocks 324 of the holding down member 32, causing the holding down member 32 to be lifted, and therefore the pressure feet 325 of the holding down member 32 are disengaged from the metal conducting blades 61 of the inserted electric plug 6. In an alternate form of the electric socket locking structure, the knob 31 has a bottom screw rod 311′ adapted for locking the inserted electric plug. When rotating the knob of the locking device of the electric socket locking structure, the holding down block 32′ is moved upwards or downwards between the unlocking position and the locking position. According to this design, the use of the knob 31 requires much device space in vertical direction. The operation control is not simple. Further, forcing the pressure feet 325 of the holding down member 32 to hold down the metal conducting blades 61 of the inserted electric plug 6 affects the plugging and unplugging force of the electric plug, causing the internal conducting metal terminals 4 in the electric socket to be damaged easily. Further, because the conducting metal terminals 4 are shaped like a fork for the contact of the metal conducting blades 61 of the inserted electric plug 6 at right angles. This contact manner produces a high contact resistance, resulting in a temperature rise.
U.S. Pat. No. 6,428,339 discloses an electric socket design, entitled “Lockable electrical cord connector unit”. According to this design, the lockable electrical cord connector unit comprises a cylindrical connector housing made of electrically non-conductive material, a locking control ring telescoping over the connector housing and mechanically connected to structure within the connector housing that allows male electrical connector members extending from the housing to be locked into a female electrical socket. The locking ring allows both ends to be locked to mating electrical terminals. However, the operation of this design is inconvenient.
U.S. Pat. No. 6,676,428 discloses an electric socket design, entitled “Securing device for electrical connectors”. According to this design, a cylindrical wheel (100) is arranged at the top side of a housing member (22). By means of rotating the cylindrical wheel (100), a screw-style plunger (42) is moved between two prongs (24;26), thereby locking the electric plug. However, using the screw-style plunger to force the prongs affects the application of force to plug/unplug the electric plug. In consequence, the prongs inside the electric socket tend to be damaged, shortening the work life of the electric socket.
U.S. Pat. No. 7,114,979 discloses an electric socket design, entitled “Structure of conductive sheet in socket”. According to this design, a conductive sheet in a socket comprises a conductive sheet body having a conductive terminal on the rear end and two parallel conductive pins on the front end with an inserting slot formed therebetween. However, the conductive sheet in a socket is adapted to contact the inserted conductive sheet in the inserted plug at right angles. The limited contact area between the conductive sheet in the socket and the conductive sheet in the plug produces a high contact resistance, resulting in a temperature rise.